I don’t know what your climate is but up here rocks work their way to the surface due to the effects of frost. The water in the soil expands when it freezes which has the effect of pushing rocks upward with the soil, then when the ground thaws, the rocks don’t go back down as much as the soil does, and so slowly rocks make their way to the surface. This is why New England is full of stone walls, The farmers had to dispose of the stones somehow.